‘Iron-breathing’ microbe which eliminate toxic sulfide from Earth discovered by scientists

An international research team led by microbiologists Marc Mussmann and Alexander Loy at the University of Vienna has identified a previously unknown form of microbial metabolism in which bacteria use iron minerals to eliminate toxic sulfide from their environment.

The newly discovered microorganisms, known as MISO bacteria, "breathe" iron minerals by oxidizing hydrogen sulfide, a toxic gas found in oxygen-free environments. The findings were published in Nature on August 27, 2025.

The research team found that the reaction between hydrogen sulfide and solid iron minerals is not purely chemical but also biological. Microbes living in marine sediments and wetlands remove harmful sulfide from their surroundings and use it to fuel their growth.


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"We show that this environmentally important redox reaction is not solely chemical," explains Alexander Loy, research group leader at CeMESS, the Centre for Microbiology and Environmental Systems Science at the University of Vienna. "Microorganisms can also harness it for growth."

The newly discovered microbial energy metabolism, termed MISO, couples the reduction of iron(III) oxide with the oxidation of sulfide. Unlike chemical reactions, MISO directly produces sulfate, bypassing intermediate steps in the sulfur cycle.

MISO bacteria may help prevent ocean dead zones

This natural mechanism may help limit the spread of oxygen-depleted "dead zones" in oceans and lakes where marine life cannot survive.

"MISO bacteria remove toxic sulfide and may help prevent the expansion of so-called 'dead zones' in aquatic environments, while fixing carbon dioxide for growth – similar to plants," adds Marc Mussmann, senior scientist at CeMESS.

Biogeochemical cycles regulate Earth's climate and element movement

The movement of elements such as carbon, nitrogen, sulfur, and iron through Earth's systems is governed by biogeochemical cycles. These cycles involve chemical reactions called redox reactions that transfer elements between the atmosphere, oceans, soil, rocks, and living organisms.

Microbes are vital to these global processes, using compounds like sulfur and iron to produce energy in ways similar to how humans use oxygen. Sulfur and iron are especially important for microorganisms that live in low-oxygen environments like the seafloor or wetlands.

When microbes consume sulfur, they often change the chemical form of iron simultaneously. This connection between the sulfur and iron cycles affects nutrient flow and the production or breakdown of greenhouse gases such as carbon dioxide and methane.

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Microbial process faster than chemical reactions in laboratory tests

In laboratory growth experiments with a cultivated MISO bacterium, researchers demonstrated that the enzymatically catalyzed reaction is faster than the equivalent chemical reaction. This suggests that microbes are the primary drivers of this process in nature.

"Diverse bacteria and archaea possess the genetic capacity for MISO," explains Song-Can Chen, lead author of the study, "and they are found in a wide range of natural and human-made environments."

MISO accounts for 7% of global sulfide oxidation

In marine sediments, MISO could account for up to 7% of global sulfide oxidation to sulfate, driven by the substantial flux of reactive iron from rivers and melting glaciers into the oceans.

Hydrogen sulfide production occurs in oxygen-free habitats

In oxygen-free habitats such as marine sediments, wetlands, and underground aquifers, specialized microbes produce hydrogen sulfide, a toxic gas with a distinct odor reminiscent of rotten eggs.

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The interaction between sulfide and solid iron(III) oxide minerals—like rust—helps regulate how much sulfide accumulates in these settings. Until now, scientists believed this process was entirely abiotic, driven only by chemical reactions that produce compounds like elemental sulfur and iron monosulfide (FeS), the black mineral responsible for the dark coloration often seen in low-oxygen coastal or beach sediments.

The findings of the University of Vienna team, supported by the Austrian Science Fund (FWF) as part of the 'Microbiomes Drive Planetary Health' Cluster of Excellence, reveal a previously unknown biological mechanism that links sulfur, iron, and carbon cycling in oxygen-free environments.

"This discovery demonstrates the metabolic ingenuity of microorganisms and highlights their indispensable role in shaping Earth's global element cycles," Alexander Loy concludes.